Fuel burner control system



Jan. 12, 1943. a M. MILLER 2,308,295

FUEL BURNER CONTROL SYSTEM Filed May 51, 1940 CLOSED COLD 67 ovzueo HOT finnenfox firnesa M. Miller Patented .lan. 12, 1943 FUEL BURNER CONTROL SYSTEM Ernest lVl. Miller, Excelsior, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application May 31, 1940, Serial No. 338,081 4 Claims. (CL 158-438) This invention is directed generally to automatic control systems foriluid iuel burners, and more particularly to simplified systems in which a minimum number of parts are used which provide all of the necessary features of safety.

One of the main objects of this invention is to provide a fuel burner control system utilizing a single relay and two wire closed cold combustion responsive switch which is so arranged as to render the system safe on ignition or flame failure and also to interpose a time delay between successlve burner operations in order to provide for the proper scavenger periods.

Another object is to arrange the above system so that it will check itself against a burned out safety switch heater. 1

Another object is to provide a control which accomplishes the above results by pulling in the relay through the combustion switch and safety switch heater, and then connecting the relay in parallel with the combustion switch and heater so that as the heater circuit is broken. when the switch opens in response to combustion, the relay will remain energized.

Still another object is to arrange the above system so that the holding circuits for the relay and safety switch heater are made substantially simultaneously with the breaking of the original energizing circuit.

These and other objects will readily become apparent as the following specification is read in the light of the accompanying drawing in which the single figure diagrammatically illustrates a fuel burner control system embodying my invention.

The reference numeral Hi indicates generally the usual room thermostat which is located in the space whose temperature is being controlled. This room thermostat comprises a bimetallic element II which carries a pair of resilient contact blades l2 and i3 which cooperate respectively with the stationary contacts H and ii. The com tact blades are so arranged that on a decrease in temperature the contact blade I! will engage contact M and then flex to permit the contact blade I! to engage the contact I! on a further decrease in temperature.

This control system is also provided with the usual safety switch indicated generally at H, which comprises a pair of resilient contact blades II and I! which are biased to open position but are normally latched in closed position by the free end of the bimetallic element 20. An electric heater 2| is located adjacent the bimetallic element and when this heater is energized for 5 former a predetermined period of time it causes the bimetallic element to warp toward the left sufliciently to release the blades I8 and i9 and permit them to move to open circuit position. It is contemplated that this safety switch shall be provided with the usual trip free reset mechanism which is manually operated to reset and latch the switch in closed position. This reset mechanism forms no part of the present invention and as such devices are well recognized in this art a description of the same is not deemed necessary.

The control system is further provided with a relay coil 23 which isadapted to actuate an as:- mature indicated by the dotted line 24. Connected to the armature is a first switch arm 25 carrying a pair of contact blades 2% and 27 which are adapted to cooperate with stationary contacts 2B and 29, respectively. when the relay is deenergized as shown in the drawing contact blade 28 is in engagement with contact 28 and upon energization of the relay coil 23 the armature it causes the contact blade 26 to separate from contact 28 and the contact blade ill engage contact 28. The armature 24 also actuates contact arms 30 and 3| which are in open circuit position when the relay is deenergized as shown and which, upon energization of the relay, are moved into engagement with the stationary con- 30 tacts 32 and 33, respectively. The parts must be so arranged that the contact arm 38 and com tact blade 27 must engage their stationary contacts substantially simultaneously with the disengagement of contact 28 by the contact blade 28.

Indicated generally at 35 is a combustion responsive switch comprising a switch arm 36 and stationary contact it. It is intended that the arm 38 be'actuated by a device responsive to combustion through a slip friction connection or other suitable arrangement so that the arm 38 will be moved in response to the presence or absence combustion rather than its movement all being dependent upon any particular temperature. Any arrangement for accomplishing this function is obviously suitable for use with this system. In this case the device 35 is so arranged that the arm 38 will engage contact 31 in the absence of combustion and will separate in the presence of combustion.

ii, the primary winding 12 of which is connected to the supply conductors 43 and 66 by means of the electrical conductors 65 and 46.

Operation The drawing shows the parts in the position which they will assume when the room thermostat i is satisfied and has been satisfied for a sufiicient length of time to permit the combustion responsive switch 36, 31 to close. It will be noted at this time that the relay coil 23 is deenergized and all of the relay switches are open with the exception of the switch 26, 26. The burner motor and ignition device are both deenergized and the room thermostat i6 is maintaining the switches l2, I4 and |3, IS in open circuit position. There is no heat being developed in the combustion chamber of the furnace and as a result the temperature in the room in which the thermostat I0 is located will begin to drop. The bimetallic element U will therefore contract and first cause the contact blade |2 to engage the stationary contact II. This will have no effect upon the control system at this time. A further decrease in temperature will cause the contact blade |3 to engage the stationary contact i5. This will establish a circuit from the secondary winding 50 of the transformer ll through conductor switches l2, l4 and |3, |5, conductor 52, switch 26, 26, conductor 53, relay coil 23, conductors 54 and 55, combustion responsive switch 36, 31, conductor 56, safety switch heater 2|, conductor 51, safety switch l8, l3 and conductor 58 back to the secondary winding 50.

As a result of the establishment of this circuit the relay coil 23 will be energized and will therefore pull in its armature 26. As the armature 26 is pulled in the switch 26, 28 will open thereby breaking the original energizing circuit traced above. At substantially the same time however the switches 21, 29 and 30, 32 will be closed establishing the following holding circuit for the relay coil 23. From the secondary winding 50, conductor 5|, switch l2, l6, bimetallic element conductor 60, switch 30, 32, conductors 6| and 54, relay coil 23, conductor 53, switch 21, 29, conductor 62, safety switch l6, l6, and conductor 58 back to the secondary winding 50. It will be seen that this circuit will maintain the relay coil energized independently of the combustion responsive switch 36, 31, andthe original energizing switch 26, 28. It will be noted that for a very brief instant the relay coil 23 will be deenergized. This is due to the fact that it is practically impossible to have the switches 30, 32 and 21, 29 make at exactly the same instant that the switch 26, 26 breaks. The momentum of the armature 26 as it is pulled in by the relay coil 23 is sufficient however to assure the closing of the two switches 30, 32 and 21, 29 upon energization of the relay coil 23. It is immaterial switch heater having been burned out.

switch heater 2|, conductor 51, safety switch l3, l9, and conductor 53 back to the secondary winding 50. It will thus be seen that when the relay 23 pulls in the relay coil and the safety switch heater will be connected in parallel across the secondary winding 56.

As the relay pulls in it also closes switch 3 I, 33. This connects the burner motor 36 across the line by conductors 65, 66, and 61. The ignition device is connected in parallel with the burner motor by conductors 63 and 69. The energization of the burner motor and ignition device will normally establish combustion. The safety switch heater 2| will remain energized until combustion is established and the switch 36, 31 opened deenergizing the heater. This is the normal running condition of the circuit.

If combustion should not be established upon the energization of the burner motor and ignition device then the combustion responsive switch 36, 31 will remain closed and after a predetermined length of time the heater 2| will cause the thermostat 20 to unlatch the safety switch |6, |9 thereby deenergizing the relay coil 23 and opening the circuit to the burner motor 36 and ignition device 40. If a flame failure should occur while the device is running the combustion responsive switch 36, 31 will close and reenergize the safety switch heater 2| which after a predetermined length of time will cause the thermostat 20 to unlatclythe safety switch l6, l3.

If a momentary power failure should occur while the device is running the relay 23 will drop out and cannot bepulled in again until the combustion responsive switch 36, 31 has cooled and reclosed. The chling of the combustion responsive switch therefore times the scavenger period between successive burner energizations and protects against explosions due to the oper- 'ation of the ignition device while the combustion chamber is full of unburned fuel.

It will therefore be seen that I have provided an oil burner control system which utilizes a single electromagnetic relay and two wire closed cold combustion switch and that this system protects against ignition and flame failure, provides the proper scavenger period between successive burner energizations on a momentary power failure or thermostat action and also checks at each operation against the safety The latter is true because the original circuit energizing the relay coil 23 passes directlythrough the to the successful operation of this relay whether the two switches make just before or just after he breaking of the switch 26, 26. The ideal operation would be for these actions to occur simultaneously but as stated above this is practically impossible.

At the time the relay coil 23 is energized to close the holding circuit for itself as traced safety switch heater 2|.

It is obvious that if an intermittent ignition system is desired a. switch conductor 66 or 66 in series with the ignition device may be actuated in some suitable manner such as by the combustion responsive device which operates the switch arm 36. V

Various changes and modifications ofthis invention will doubtless occur to those who are skilled in the art and I therefore desire to be limited only by the scope of the appended claims and not by the specific embodiment of the invention disclosed herein.

I claim as my invention:

1. A fuel burner control system comprising in combination, electrical fuel supplying means, a relay which upon energization renders said means operative to supply fuel for combustion, a closed cold combustion responsive switch, a safety switch and heater therefor, a main control switch, an energizing circuit for said relay including said main switch, combustion switch, and

' an energizing circuit for said relay safety switch heater, and means operated by said relay breaking the original energizing circuit but keeping said safety switch heater energized by connecting said relay in parallel with said combustion responsive switch and safety switch heater, said combustion responsive switch opening in response to combustion to deenergize said safety switch heater.

2. A fuel burner control system comprising in combination, electrical fuel supplying means, a relay which upon energization renders said means operative to supply fuel for combustion, first, second, and third switches, said relay when deenergized closing said first switch and when energized closing said second and third switches, a closed cold combustion responsive switch, a safety switch and heater therefor, a main switch, including said main switch, first switch, combustion responsive switch, and safety switch heater in series, said relay upon energization establishing a holding circuit for itself including said main switch, second switch, and third switch in series, and a parallel circuit including said main switch, second switch, combustion responsive switch, and safety switch heater in series, said combustion responsive switch opening in response to combustion.

3. A fuel burner control system comprising in combination, electrical fuel supplying means, a

relay which upon energization renders said to supply fuel for combustion,

means operative first, second, and third switches, said relay when deenergized closing said first switch and when energized closing said second and third switches, said second and third switches being closed sub stantially simultaneously with the opening of the first switch, a closed cold combustion responsive switch, a safety switch and heater therefor, a main switch, an energizing circuit for said relay including said main switch, first switch, combustion responsive switch, and safety switch heater in series, said relay upon energization establishing a holding circuit for itself including said main switch, second switch, and third switch in series, and a parallel circuit including said main switch, second switch, combustion responsive switch, and safety switch heater in series, said combustion responsive switch opening in response to combustion.

4. A fuel burner control system comprising in combination, electrical fuel supplying means, a relay which, when energized, renders said means operative to supply fuel for combustion, a closed cold combustion responsive switch, a safety switch in control of the supply of power to said relay, a heater for said safety switch, a main control switch, a circuit for said relay including said main switch, combustion switch and safety switch heater, 9. source of power, a pair of conductors connecting said circuit to said source of power for energizing said circuit, and means operated by said relay closing a running circuit for said relay independent of said combustion responsive switch and safety switch heater, said pair of conductors connecting said holding circult to said source of power, said combustion responsive switch opening in response to combustion to deenergize said safety switch heater, and reclosing upon a flame failure to immediately reenergize said safety switch heater.

ERNEST M. MILLER, 

